The side wall of a glass container can include various types of defects, including an area of unevenness in glass distribution which will provide a lensing effect when backlit (a refractive defect). Container inspection machines, such as shown in U.S. Pat. No. 5,004,909, inspect the sidewall of a glass bottle by presenting the bottle in front of a light source defined by alternating black and white stripes. Such an inspection machine can find refractive best when they are located at the edge of the stripe. Container inspection machines, such as shown in U.S. Pat. No. 4,601,395, inspect the sidewall of a glass container by presenting the bottle in front of a light source defined by a single bright area that is always in the view of the camera, with transversely spaced outer regions of various intensities and rotating the container.